Heat oven to 350 degrees F. Place a paper baking cup or silicone cup in each of the 24 cupcake wells of the muffin pan; set aside.
In large bowl, beat all white cake ingredients together (except egg whites) until just combined.
Beat in egg whites for 2 minutes. Pour batter into baking pan.
Bake 15 to 20 minutes or until a toothpick inserted in center of cupcakes come out clean. Cool 10 minutes in pan before removing to a wire rack for additional cooling.
Meanwhile, in a 2-quart saucepan, melt butter over medium-high heat until butter becomes a dark golden brown (amber color) with a nutty aroma, 3 to 5 minutes. Watch closely to prevent burning of the butter.
Add brown sugar and boil for 1 minute, whisk continuously. Decrease heat to medium and add half-and-half and Kosher salt. Continue whisking for 2 minutes. Add more salt if needed.
Remove from heat and reserve 3 tablespoons of brown butter salted caramel in a small bowl; set aside.
Allow the remaining caramel to cool till warm to the touch. Add 2 cups of confectioner's sugar and whisk until just combined. Note: some brown sugar-caramel clumps may be seen which is ok.
Place a large dollop of frosting onto cupcakes and spread to create dome-shaped tops.
Before the frosting dries, randomly place popcorn onto the applied frosting.
Reheat reserved caramel if necessary by heating in the microwave for 15 seconds. Drizzle caramel above popcorn cupcakes. Repeat process with remaining cupcakes. ENJOY!